Modeling Bulk Atmospheric Drainage Flow in a Valley

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  • 1 Atmospheric Turbulence and Diffusion Division NOAA/ARL, Oak Ridge, Tennessee
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Abstract

Most simulations of bulk valley-drainage flows depend heavily on parameterizations. The 1984 Atmospheric Studies in Complex Terrain (ASCOT) field experiment in Brush Creek Valley, Colorado, provided an unprecedented density of measurements in a natural valley of simple shape, allowing tests of assumptions and parameterizations developed from laboratory measurements and detailed numerical simulations. This paper uses the ASCOT data to test a model that computes total fluxes of mass (volume) and momentum—determining buoyant and pressure-gradient forces from measured temperature profiles, and parameterizing drag, entrainment, and sidewall and tributary drainage. Computed divergences of volume and momentum flux are within a factor of 2 of the Doppler lidar measurements in Brush Creek Valley. The relative importance of individual terms as parameterized in the model is discussed. A major problem for future work is the treatment of the interaction between valley drainage and ambient flow.

Abstract

Most simulations of bulk valley-drainage flows depend heavily on parameterizations. The 1984 Atmospheric Studies in Complex Terrain (ASCOT) field experiment in Brush Creek Valley, Colorado, provided an unprecedented density of measurements in a natural valley of simple shape, allowing tests of assumptions and parameterizations developed from laboratory measurements and detailed numerical simulations. This paper uses the ASCOT data to test a model that computes total fluxes of mass (volume) and momentum—determining buoyant and pressure-gradient forces from measured temperature profiles, and parameterizing drag, entrainment, and sidewall and tributary drainage. Computed divergences of volume and momentum flux are within a factor of 2 of the Doppler lidar measurements in Brush Creek Valley. The relative importance of individual terms as parameterized in the model is discussed. A major problem for future work is the treatment of the interaction between valley drainage and ambient flow.

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